Electron beam control system

ABSTRACT

An electron beam control system for apparatus employing a color cathode ray tube of in-line beam type in which a plurality of electron beam pass through a magnetic field for beam dynamic convergence and are given with deformations of the shape of cross-section thereby, which system includes a magnetic device for producing an additional magnetic field, through which the electron beams pass before arriving at the magnetic field for beam dynamic convergence, for acting on the shape of cross section of the electron beams so as to compensate for the deformation caused by the magnetic field for beam dynamic convergence.

United States Patent 11 1 Saito et al.

[ 51 Aug. s, 1975 1 1 ELECTRON BEAM CONTROL SYSTEM [75] Inventors: Tsunenari Saito; Yoshio Aoki. both of Tokyo, Japan [30] Foreign Application Priority Data Feb 2 1973 Japan 48-14681111 1 [52] US. Cl. 1, 315/370; 315/31 R [51] Int. Cl. H01] 29/56 [58] Field of Search 1. 315/13 C 13 CG, 27 OD 315/27 XY, 31, 371, 368, 370. 382

[56] References Cited UNITED STATES PATENTS 1462.638 8/1969 Tetsuo et a1. 315/13 C 3,735 l89 5/1973 Karlovics 315/13 C Primary Examiner-Maynard R. Wilbur Assistant Examiner-T. M1 Blum Attorney, Agent, or Fz'rm-Lewis H. Eslingcr; Alvin Sinderbrand [5 7 1 ABSTRACT An electron beam control system for apparatus employing a color cathode ray tube of in-line beam type in which a plurality of electron beam pass through a magnetic field for beam dynamic convergence and are given with deformations of the shape of cross-section thereby, which system includes a magnetic device for producing an additional magnetic field, through which the electron beams pass before arriving at the magnetic field for beam dynamic convergence, for acting on the shape of cross section of the electron beams so as to compensate for the deformation caused by the magnetic field for beam dynamic convergence.

6 Claims, 8 Drawing Figures PAltNltU (PRIOR ART) ELECTRON BEAM CONTROL SYSTEM BACKGROUND OF THE INVENTION l Field of the Invention This invention relates generally to an electron beam control system for use with a cathode ray tube, and more particularly to an electron beam shape control system for use with in-line type color cathode ray tube for dynamic correction of beam shape deformation.

2. Description of the Prior Art A dynamic convergence device is necessary for a color cathode ray tube. Conventionally, a magnetic type dynamic convergence device is used for converging three electron beams on the screen of the cathode ray tube. However, in this case the shape of the electron beams is deformed by a magnetic field of the magnetic type convergence device, and hence the resolution of a reproduced picture on the screen of the cath ode ray tube is aggravated.

SUMMARY OF THE INVENTION This invention provides an electron beam control system for use with an in-line type color cathode ray tube for dynamic correction or compensation of electron beam shape deformation.

A color cathode ray tube with the electron beam control system of this invention has a dynamic convergence device composed of a pair of two-pole magnetic yokes aligned in horizontal and a beam shape correction or compensation coil composed of a pair of two pole magnetic yokes aligned in vertical. In this case. a parabolic signal is supplied to the dynamic convergence coil and the beam shape correction coil commonly to produce magnetic fields contrary in pole with each other, thereby correcting or compensating for a deformation of the electron beam shape caused by a magnetic field of the dynamic convergence coil.

Accordingly, it is an object of this invention to provide an electron beam control system free from the defect encountered in the prior art.

It is another object of the invention to provide an electron beam control system with electron beam compensating device so as to compensate for the deformation of electron beams in beam spot size.

The other objects, features and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a plane sectional view of an in-line type color cathode ray tube of the prior art;

FIG. 2 shows a sectional view taken on the line aa in FIG. I;

FIG. 3 shows a waveform chart of a dynamic conver gence current used for the cathode ray tube of FIG. 1;

FIG. 4 shows a cross section of an electron beam when no dynamic convergence current flows in a dynamic convergence coil of the cathode ray tube of FIG. 1;

FIG. 5 shows a cross section of an electron beam when the dynamic convergence current flows in the dynamic convergence coil of cathode ray tube of FIG. 1',

FIG. 6 is a graphic diagram showing the relationship between the dynamic convergence current and a beam spot size of the electron beam. and between a correction current and a beam spot size of the electron beam, respectively;

FIG. 7 shows a plane sectional view of an in-line type color cathode ray tube with the electron beam control system according to this invention; and

FIG. 8 shows a sectional view taken on the line b-b in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to better understand the present invention, an example of the prior art will be firstly described.

FIG. 1 shows an embodiment of the in-line type color cathode ray tube of the prior art.

In the embodiment of FIG. 1, red, green and blue cathodes K K and K are arranged sequentially to be aligned substantially in a common horizontal plane and first to fifth grids G to G are coaxially and sequentially arranged common to the cathodes K K and K Red, green and blue electron beams R, G and B emitted from the cathodes K K and K are prefocused by a subsidiary electron lens L formed by the second and third grids G and G to cross over at the center of a main electron lens L formed by the third to fifth grids G to G substantially and thereafter to diverge. On the divergence way of electron beams R, G and B and in the neck portion of the cathode ray tube, there is provided a static convergence device or means I which consists of a pair of inner convergence plates 2 and 3 and a pair of outer convergence plates 4 and 5. The inner convergence plates 2 and 3 are supplied with an anode voltage E while the outer convergence plates 4 and 5 are supplied with a convergence voltage E which is lower than the anode voltage E,, by several hundred volts to perform the static convergence operation. At the position where the static convergence device 1 is provided in the neck portion of the cathode ray tube, there is provided a dynamic convergence yoke 6 outside the neck portion. By flowing a parabolic current with the horizontal period through the dynamic convergence yoke 6, a predetermined magnetic field is originated therefrom to converge the three electron beams R, G and B on the luminescent screen (not shown) of the color cathode ray tube. In FIG. 1, reference numeral 7 indicates a horizontal and vertical deflection device.

As shown in FIG. 2, the dynamic convergence yoke 6 consists of, for example, a pair of two-pole electromagnetic elements which include U-shaped cores 8 and 9, and coils l0 and II which are wound on the cores 8 and 9, respectively. The coils l0 and 11 are aligned in the horizontal plane around the neck portion of the cathode ray tube. When the parabolic signal i shown in FIG. 3, is supplied to flow through the coils l0 and 11, the dynamic convergence yoke 6 produces a four pole magnetic field as shown in FIG. 2 for moving side electron beams of three electron beams in the opposite directions in the horizontal plane.

In this case, if the dynamic convergence current is zero, each beam spot shape of the three electron beams on the screen becomes to a circular one as shown in FIG. 4 which is minimum in cross section area or size. (In FIG. 4, only one of the three beam spots is shown.) However, as the dynamic convergence current increases, a magnetic field H, in the vertical direction is produced and a magnetic field H in the horizontal direction is also produced. As a result. a force F, which acts on the respective beams for stretching the same in the horizontal and a force F which acts on the respective beams for pressing the same in the vertical direction are generated as shown in FIG. 2 which is viewed from the cathodes, and consequently each beam spot shape of the three electron beams on the screen is deformed in a diamond shape as shown in FIG. 5 and increases in cross-sectional area or beam spot size. Although FIG. 5 shows only one deformed beam spot, it is appreciated that the other two beam spots (not shown) are similarly deformed. Accordingly, a reproduced picture is deteriorated in resolution.

FIG. 6 shows a graph of the relationship between the dynamic convergence current and the beam spot size on the screen and between a correction current and the beam spot size, respectively, in which the ordinate represents the beam spot size m (where 0 indicates the horizontal size of the beam spot and b the vertical size of the beam spot) and the abscissa the dynamic convergence and correction currents I in mA.

In the graph of FIG. 6, a curve 12 shows the beam spot size variation in response to the variation of the dynamic convergence current I flowing through the dynamic convergence yoke 6.

An embodiment of the electron beam control system according to this invention, which may compensate for the above mentioned deformation of the electron beam spot positively, will be now described with reference to FIG. 7 which illustrates a color cathode ray tube employing the electron beam control system of this invention and hence in which reference numerals and symbols same as those used in FIGS. 1 and 2 designate the same elements.

With this invention, as shown in FIG. 7, a correction or compensation yoke 13, which may produce a magnetic field opposite in polarity with respect to the magnetic field produced by the dynamic convergence yoke 6, is provided outside the neck portion of the cathode ray tube and in the vicinity of the main electron lens L in the tube axis. By way of example, the correction yoke 13 can be a pair of two-pole electro-magnetic ele ment similar to the dynamic convergence yoke 6.

An example of the correction yoke 13 will be now described with reference to FIG. 8. As shown in FIG. 8, cores l4 and 15, which are substantially same as the cores 8 and 9 of dynamic convergence yoke 6 in shape, are disposed around the neck portion in the vicinity of the main electron lens L such that the cores 14 and 15 are opposed to each other with gripping the neck portion therebetween in the vertical direction. Further, coils l6 and 17 are wound on the cores l4 and 15, re spectively, same in number as the coils l0 and 11 of yoke 6. In this case, the coils l0 and ll of the yoke 6 and the coils l6 and 17 of the yoke 13 are connected in series, as shown in FIG. 8, and a dynamic convergence voltage e is impressed across the both ends of series connected coils to produce correction or com pensation magnetic fields H and H in the horizontal and vertical directions which are opposite in direction to the fields H, and H produced by the yoke 6.

With the color cathode ray tube described in connection with FIGS. 7 and 8, forces for acting on the electron beams to press the same in the horizontal direction and acting on the electron beam to stretch the same in the vertical direction are caused previously at the position of the main electron lens L, by the correction yoke 13. and the forces acting on the electron beam to stretch the same in the horizontal direction and acting on the electron beam to press the same in the vertical direction are caused during the time when the electron beam passes through the convergence plates 2 to 5, as described previously. As a result, the beam spots of the respective electron beams on the screen are subjected to no deformation and hence the beam spots can be same as that shown in FIG. 4 which is circular in cross section and minimum in size.

With this invention, since the correction yoke 13 is provided in the vicinity of the main electron lens L where the three electron beams cross-over, the correction magnetic field acts on the three electron beams equally and the correction yoke 13 does not affect the dynamic convergence operation caused by the dynamic convergence yoke 6 or the predetermined dynamic convergence operation is achieved as it is.

According to the experiments in which the coils l6 and 17 of correction yoke 13, which are connected as shown in FIG. 8 together with the coils 10 and 11 of the yoke 6, are supplied with a current same as that applied to the coils l0 and 11 of dynamic convergence yoke 6 in absolute value, it is ascertained that the deformation of the beam spot size on the screen at respective positions is perfectly corrected or compensated for, as shown by a line 18 in FIG. 6.

The above description is given on the case that the coils of the dynamic convergence yoke and those of the correction yoke are connected in series, but it may be possible that they are connected in parallel with the same effect.

The above description is given to only one preferred embodiment of this invention, but it may be apparent that many modifications and variations could be effected by those skilled in the art without departing from the spirits and scope of the novel concepts of the present invention. Accordingly, the scope of the invention should be determined by the appended claims only.

We claim as our invention:

1. An electron beam control system for apparatus utilizing a color cathode ray tube comprising:

a. a color cathode ray tube having a luminescent screen, beam generating means for emitting a plurality of electron beams to said screen, all of said electron beams being aligned substantially in a common plane, and an electron focus lens disposed between said beam generating means and said screen having a substantially central portion at which said electron beams cross over;

b. beam deflecting means disposed between said beam generating means and said screen, said beam deflecting means producing a magnetic field through which said electron beams pass for moving said electron beams in a direction parallel to said common plane, said magnetic field affecting deformation of the cross-sectional shape of each of said electron beams; and

c. means for compensating for the cross-sectional shape deformation of each of the electron beams including a magnetic yoke disposed around the substantially central portion of said electron focus lens, said magnetic yoke producing an additional magnetic field through which each of said electron beams pass for acting on the cross-sectional shape of each of said electron beams so as to compensate for the deformation caused by the magnetic field of said beam deflecting means.

2. An electron beam control system according to claim 1, wherein said beam deflecting means comprises with respect to the magnetic field produced by said dynamic convergence means to thereby exert a force on each of said electron beams that is opposite to the force exerted thereon by the magnetic field produced by said dynamic convergence means.

5. An electron beam control system according to claim 3, wherein said dynamic convergence means is mounted around said static convergence means.

6. An electron beam control system according to claim 4, wherein a dynamic convergence signal is supplied in common to said dynamic convergence means and said beam deformation compensating means. 

1. An electron beam control system for apparatus utilizing a color cathode ray tube comprising: a. a color cathode ray tube having a luminescent screen, beam generating means for emitting a plurality of electron beams to said screen, all of said electron beams being aligned substantially in a common plane, and an electron focus lens disposed between said beam generating means and said screen having a substantially central portion at which said electron beams cross over; b. beam deflecting means disposed between said beam generating means and said screen, said beam deflecting means producing a magnetic field through which said electron beams pass for moving said electron beams in a direction parallel to said common plane, said magnetic field affecting deformation of the cross-sectional shape of each of said electron beams; and c. means for compensating for the cross-sectional shape deformation of each of the electron beams including a magnetic yoke disposed around the substantially central portion of said electron focus lens, said magnetic yoke producing an additional magnetic field through which each of said electron beams pass for acting on the cross-sectional shape of each of said electron beams so as to compensate for the deformation caused by the magnetic field of said beam deflecting means.
 2. An electron beam control system according to claim 1, wherein said beam deflecting means comprises beam scanning means for deflecting each of said electron beams in the same direction; and dynamic convergence means having a magnetic yoke for producing a magnetic field through which each of said electron beams pass for moving said electron beams for beam dynamic convergence.
 3. An electron beam control system according to claim 2, further comprising static convergence means for statically converging said electron beams on said screen.
 4. An electron beam control system according to claim 3, wherein said beam deformation compensating means produces a magnetic field opposite in polarity with respect to the magnetic field produced by said dynamic convergence means to thereby exert a force on each of said electron beams that is opposite to the force exerted thereon by the magnetic field produced by said dynamic convergence means.
 5. An electron beam control system according to claim 3, wherein said dynamic convergence means is mounted around said static convergence means.
 6. An electron beam control system according to claim 4, wherein a dynamic convergence signal is supplied in common to said dynamic convergence means and said beam deformation compensating means. 